This invention relates to an automatic chemical mechanical polishing apparatus for polishing a substrate such as a semiconductor wafer having semiconductor device patterns.
In general, a polishing apparatus is known which is for polishing a substrate such as a semiconductor wafer having semiconductor device patterns. A conventional polishing apparatus comprises a polishing table equipped with a polishing pad and a wafer holding head for holding a wafer. The polishing table rotates at a rotating speed. The wafer is pressed onto the polishing pad at a constant pressure by lowering the wafer holding head in order to polishing the wafer. The polishing pad is refreshed by a polishing pad conditioner having fine diamond particles.
A pair of polishing tables may be used on polishing the wafer to improve a flatness and roughness of the processed surface. One of, polishing tables may be called a primary polishing table. Another one of polishing tables may be called a secondary polishing table. The primary polishing table has a crude (hard) polishing cloth as the polishing pad that is for use in a rough polishing. The secondary polishing table has a fine (soft) polishing cloth as rhe polishing pad that is for use in a final or finish polishing.
It is possible to increase the polishing speed of the wafer by increasing the polishing table rotation and the pressure on the wafer in the polishing pad. Inasmuch as scratching wounds or scars occurs on the wafer when the pressure on the wafer is too high, it is desirable that the pressure on the wafer in the polishing pad is low at a high rotating speed in order to suppress occurrence of the scratching wounds on the wafer.
The conventional polishing apparatus comprises a large-diameter polishing table compared with a diameter of the wafer. It is impossible to rotate the large-diameter polishing table at the high speed under the low polishing pressure. In addition, the diamond particles drop out of the polishing pad conditioner onto the polishing pad refreshing the polishing pad, inasmuch as the polishing pad is directed upwardly. The diamond particles dropped out of the polishing pad conditioner onto the polish pad, scratch and wound the surface of the wafer.
As described above, the primary and the secondary polishing tables may be used for highly precise polishing of the wafer. More specifically, both of the primary and the secondary polishing tables are rotated to polish the wafer. The wafer is pressed and rotated onto the primary polishing table to obtain a roughly polished wafer. The primary polished wafer is pressed and rotated onto the secondary polishing table to execute a final polishing.
In as much as the primary and secondary polishing tables are considerably large in diameter as compared to that of the wafer, the use of such large-size polishing tables would result in an increase in occupation area within factory space. This means that the space utility efficiency is reduced. Especially, the diameters of the primary and the secondary polishing tables tend to increase as the diameter of the wafer increases from 4 through 6 inches to 8 through 12 inches.
Furthermore, it is necessary to use an amount of abrasive liquid in order to uniformly lay the abrasive fluid over the entire surface of each of primary and the secondary polishing tables. On using an amount of abrasive liquid, running cost increases. An environmental problem occurs on disposing the used abrasive fluid as a waste product. In addition, a loss of time occurs in the conventional polishing apparatus inasmuch as it is necessary to transfer the wafer from the primary polishing table to the secondary polishing table.
More specifically, the wafer is gripped by a first chuck to be pressed onto the primary polishing table with abrasive fluid. On transferring the wafer from the primary polishing table to the secondary polishing table, it is necessary to release the wafer from the first chuck in order to attach the wafer to a second chuck which is associated with the secondary polishing table. When it takes a long time to attach the wafer to the second chuck, the abrasive fluid residing on the wafer dries. When the abrasive fluid dries, scratch traces may occur on the wafer. Furthermore, the wafers may be inevitably etched. In addition, it is impossible to watch the polishing surface of the wafer inasmuch as the polishing surface is directed to each of the primary and the secondary polishing tables downwardly. As a result, it is difficult to watch aspects of the wafer during polishing process. second chuck which is associated with the secondary polishing table. When it takes a long time to attach the wafer to the second chuck, the abrasive fluid residing on the wafer dries. When the abrasive fluid dries, scratch traces may occur on the wafer. Furthermore, the wafers may be inevitably etched. In addition, it is impossible to watch the polishing surface of the wafer inasmuch as the polishing surface is directed to each of the primary and the secondary polishing tables downwardly. As a result, it is difficult to watch aspects of the wafer during polishing process.
It is therefore an object of this invention to provide an automatic polishing apparatus capable of polishing a wafer with a high planarization.
According to this invention, the automatic polishing apparatus comprises:
(A) an index table for holding at least two wafers as first and second wafers at first and second predetermined locations, respectively, the index table being given a rotation at a predetermined angle around a predetermined rotation axis, each of the first and the second wafers having front surface which is directed upwardly,
(B) at least one polishing station which is positioned at a first stop position of the index table, the polishing station being a region for use in polishing each of the first and the second wafers into the polished wafer, and
(C) a polishing head located above the index table at the polishing station, the polishing head having a polishing surface which is for polishing the front surface of each of the first and the second wafers transferred to the polishing station.